Electrowetting device

ABSTRACT

An electrowetting device includes: a liquid-confining member including a base and an electrode unit supported on the base, the liquid-confining member defining an inner chamber; a first liquid of a magnetic ink disposed in the inner chamber; and a second liquid of a polar material disposed in the inner chamber and immiscible with the first liquid. The first and second liquids contact each other to define a liquid-liquid interface therebetween.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Taiwanese Patent Application No.101144994, filed on Nov. 30, 2012.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an electrowetting device, more particularly toan electrowetting device including a magnetic ink.

2. Description of the Related Art

An electrowetting device typically includes a housing and a workingliquid that is encapsulated in the housing and that changes its surfacetension when an external power source is applied to the working liquidfor controlling operation modes of the working liquid. Theelectrowetting device may be used in applications, such as displays, anoptical liquid lens, a biochip, etc.

U.S. patent application publication No. 2012/0073740 discloses a methodof making an electrowetting device. The method includes the steps of:(a) forming a surrounding wall on an upper surface of a substrate todefine a micro-chamber, the surrounding wall having an inner surfacesurrounding the micro-chamber and a top surface above the inner surface,the upper surface of the substrate being non-hydrophobic; (b) coatingthe surrounding wall and the upper surface of the substrate with ahydrophobic coating material; (c) removing a portion of the hydrophobiccoating material formed on the top surface of the surrounding wall,thereby exposing the top surface of the surrounding wall; and (d)filling a first liquid and a second liquid, which is immiscible with thefirst liquid, into the micro-chamber. The first liquid is a colored ink,and the second liquid is an electroconductive solution.

The first liquid is required to be firmly positioned at a predeterminedregion in the micro-chamber and be covered by the second liquid when thesecond liquid is introduced therein, so that the electrowetting devicecan work normally and reliably. However, since the first liquid has adensity smaller than that of the second liquid, control of the aforesaidpositioning and covering of the first liquid is relatively difficult.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a highly reliableelectrowetting device.

According to this invention, there is provided an electrowetting devicethat comprises: a liquid-confining member including a base and anelectrode unit supported on the base, the liquid-confining memberdefining an inner chamber; a first liquid of a magnetic ink disposed inthe inner chamber; and a second liquid of a polar material disposed inthe inner chamber and immiscible with the first liquid, the first andsecond liquids contacting each other to define a liquid-liquid interfacetherebetween. The electrode unit is adapted to be connected to anexternal power source for providing an electric field across theliquid-liquid interface. The liquid-liquid interface has a shape thatvaries in response to a change in the electric field across theliquid-liquid interface.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate embodiments of the invention,

FIG. 1 is a schematic diagram of the first preferred embodiment of anelectrowetting device according to the present invention;

FIGS. 2A to 2D are schematic diagrams illustrating consecutive steps ofa method of making the first preferred embodiment of the electrowettingdevice according to the present invention;

FIG. 3. is a schematic diagram of the second preferred embodiment of theelectrowetting device according to the present invention; and

FIG. 4 is a schematic diagram of the third preferred embodiment of theelectrowetting device according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates the first preferred embodiment of an electrowettingdevice according to the present invention.

The electrowetting device comprises: a liquid-confining member 2including a base 21 and an electrode unit 23 supported on the base 21,the liquid-confining member 2 defining an enclosed inner chamber 214; afirst liquid 31 of a magnetic ink disposed in the inner chamber 214; anda second liquid 32 of a polar material disposed in the inner chamber 214and immiscible with the first liquid 31. The first and second liquids31, 32 contact each other to define a liquid-liquid interface 33therebetween.

The electrode unit 23 is adapted to be connected to an external powersource (not shown) for providing an electric field across theliquid-liquid interface 33.

The liquid-liquid interface 33 has a shape that varies in response to achange in the electric field across the liquid-liquid interface 33. Itis noted that the liquid-liquid interface 33 does not vary in responseto a change in the magnetic field.

The first liquid 31 includes magnetic pigment particles and a nonpolarsolvent. In the first preferred embodiment, the nonpolar solvent of thefirst liquid 31 is made from a material selected from a hydrocarbonsolvent, such as n-hexane, dodecanese, and octadecane, or silicone oil.The first liquid 31 is hydrophobic, and can be driven by the electricfield to deform in the inner chamber 214, thereby varying the shape ofthe liquid-liquid interface 33.

The second liquid 32 is a polar solvent. In the first preferredembodiment, the second liquid 32 is water.

The magnetic pigment particles of the first liquid 31 have an averageparticle size of not greater than 50 nm, and preferably impart a desiredcolor under certain operation modes of the electrowetting device.

Preferably, the magnetic pigment particles of the first liquid 31 aremade from hydrophobic group modified ferric oxide.

In the first preferred embodiment, the liquid-confining member 2 furtherincludes a cover 22 covering the base 21. The base 21 includes: a lowersubstrate 211 that is opposite to the cover 22 in a vertical direction;a surrounding barricade 215 which extends from the lower substrate 211in the vertical direction and which cooperates with the lower substrate211 to define an inner space 216 therebetween; and a hydrophobic layer212 formed in the inner space 216. The electrode unit 23 includes alower electrode 231 provided on the lower substrate 211, and an upperelectrode 232 provided on the cover 22.

The lower electrode 231 cooperates with the upper electrode 232, thefirst and second liquids 31, 32 and the external power source (notshown) to form a circuit.

The base 21 of the liquid-confining member 2 further includes a lowerdielectric layer 210 that is formed on the lower electrode 231. Thecover 22 of the liquid-confining member 2 includes an upper dielectriclayer 220 that is formed on the surrounding barricade 215, and atransparent panel 221 that is formed on the dielectric layer 220. Theupper electrode 232 is disposed between the dielectric layer 220 and thetransparent panel 221.

It is noted that the shape of the first liquid 31 in the inner chamber214 is concave, and can be controlled by not only the electric fieldapplied thereto but also the height of the hydrophobic layer 212. Thehigher the hydrophobic layer 212, the lower will be the height of acentral portion of the first liquid 31 and the higher will be aperipheral portion of the first liquid 31 in the inner chamber 214.

The surrounding barricade 215 has a height greater than that of thehydrophobic layer 212 so as to prevent the first liquid 31 fromoverflowing out of the inner space 216.

FIGS. 2A to 2D illustrate consecutive steps of a method of making thefirst preferred embodiment of the electrowetting device according to thepresent invention. The method comprises: (a) providing the base 21 thatdefines an inner space 216 and that has an open end 217 which defines anopening 219 (see FIG. 2A); (b) applying the first liquid 31 of themagnetic ink to a predetermined region of the base 21 within the innerspace 216; (c) positioning the first liquid 31 on the predeterminedregion of the base 21 using a magnetic unit 4 that is magneticallyattractive to the first liquid 31 (see FIG. 2B); (d) filling the innerspace 216 with the second liquid 32 that is immiscible with the firstliquid 31 (see FIG. 2C); and (e) attaching sealingly the cover 22 to theopen end 217 of the base 21 and covering the opening 219 with the cover22 (see FIG. 2D).

Referring to FIG. 1, the lower electrode 231 is made from a conductorfilm of indium-tin-oxide, and has a thickness not less than 400A. Thelower dielectric layer 210 is made from SiN, and has a thickness ofaround 2000 Å. The surrounding barricade 215 is made from a photo resistmaterial, and is formed on the lower dielectric layer 210. Thehydrophobic layer 212 is made from hydrophobic compounds, and is formedon the lower dielectric layer 210 and the surrounding barricade 215.

The surrounding barricade 215 is formed on the lower dielectric layer210 using spin coating, dipping, or curtain coating techniques. In thefirst preferred embodiment, the hydrophobic layer 212 is made from aTeflon material, and is formed using spin coating techniques.

It is noted that a height difference between the hydrophobic layer 212and the surrounding barricade 215 can be controlled by controlling anamount of the hydrophobic compound used for forming the hydrophobiclayer 212, or by controlling the process of forming the surroundingbarricade 215. More specifically, to form the hydrophobic layer 212 andthe surrounding barricade 215 with a height difference therebetween, apattern of a first photoresist layer is first formed on the lowerdielectric layer 210 using photolithography processing techniques, ahydrophobic film is then formed on the first photoresist layer and thelower dielectric layer 210 exposed from the first photoresist layerusing spin coating techniques, a top portion of the hydrophobic film ona top end of the first photoresist layer is removed using mechanicalpolishing techniques, and a second photoresist layer is formed on thetop end of the first photoresist layer using photolithography processingtechniques. The first and second photoresist layers cooperatively definethe surrounding barricade 215, and the hydrophobic film defines thehydrophobic layer 212 and has a height the same as that of the firstphotoresist layer.

The magnetic unit 4 is a material selected from a permanent magnet, anelectromagnet, magnetic coils, and the like. In the first preferredembodiment, the magnetic unit 4 is a permanent magnet.

The hydrophobic group modified ferric oxide is formed by thermallydecompounding iron-oleate complex in a hydrocarbon solvent. Thehydrophobic group modified ferric oxide thus formed has lipophilicgroups so as to be dispersed uniformly in an oil solvent.

In one embodiment, the magnetic ink containing the hydrophobic groupmodified ferric oxide was formed by: mixing 36 g sodium oleate complex,80 g ethanol, 60 ml deionized water, 140 ml Hexane, and 10.8 g ferricchloride to form a first mixture; stirring the first mixture for 4 hoursat 70° C.; washing the first mixture with deionized water in aseparating funnel so as to obtain an iron-oleate complex; mixing 36 g ofthe iron-oleate complex, 5.7 g oleic acid, and 200 g 1-octadecane toform a second mixture; heating the second mixture to 320° C. in aheating rate of 5° C. per minute and maintaining the temperature at 320°C. for 30 minutes; cooling the second mixture; and mixing the secondmixture and a non-polar solvent so as to form the magnetic ink.

The application of the first liquid 31 in the inner space 216 may beconducted using inkjet printing techniques. The filling of the secondliquid 32 in the inner space 216 to cover the first liquid 31 may beconducted using inkjet printing techniques.

FIG. 3 illustrates the second preferred embodiment of the electrowettingdevice according to the present invention. The second preferredembodiment differs from the previous preferred embodiment mainly inthat, in this preferred embodiment, the liquid-confining member 2defines a plurality of unit cells each of which defines an inner chamber214 that receives the first and second liquids 31, 32 therein. A gap φis formed between the top end of the surrounding barricade 215 and a topregion 223 of the cover 22, such that fluid communication of the secondliquid 32 between two adjacent ones of the inner chambers 214 of theunit cells is permitted through the gap φ.

FIG. 4 illustrates the third preferred embodiment of the electrowettingdevice according to the present invention. The third preferredembodiment differs from the first preferred embodiment in that the base21 further includes a hydrophilic wall 218 which extends between andinterconnects the surrounding barricade 215 and the upper dielectriclayer 220 and which cooperates with the upper dielectric layer 220 ofthe cover 22, the hydrophobic layer 212 and the surrounding barricade215 to define the inner chamber 214. FIG. 4 also illustrates anoperating state of the electrowetting device, where the first liquid 31,which acts as a valve, is disposed at an opening position.

The inclusion of the hydrophilic wall 218 in the liquid-confining member2 permits an increase in an aperture ratio of the first liquid 31, whichis formed with a central opening 5 when disposed at the openingposition, so as to increase the resolution and the contrast ratio of theelectrowetting device.

The hydrophilic wall 218 may be made from polyimide, and may be formedon the surrounding barricade 215 by photolithographic processing andetching techniques.

The method of making the third preferred embodiment differs from themethod of making the first preferred embodiment mainly in the inclusionof an additional step (f) of forming the hydrophilic wall 218 and theimplementation of the filling of the second liquid 32 and the closing ofthe opening 219 in the aforesaid steps (d) and (e). Specifically, in themethod of making the third preferred embodiment, steps (f), (d), and (e)are conducted by: forming the hydrophilic wall 218 on the cover 22 byphotolithographic processing and etching techniques such that thehydrophilic wall 218 cooperates with the cover 22 to define a recess;filling the second liquid 32 in the recess; inverting the base 21 whichis filled with the first liquid 31 that is positioned by the magneticunit 4; and attaching the surrounding barricade 215 of the base 21 to atop end of the hydrophilic wall 218 and re-inverting the base 21, suchthat the base 21 is disposed below the recess so as to permit the secondliquid 32 to flow into the inner space 216 and the cover 22 to cover theopening 219.

Since the first liquid 31 is made from the magnetic ink, the same can bepositioned in the inner space 216 by the magnetic unit 4 during fillingof the second liquid 32 in the inner space 216, thereby preventingundesired malposition of the first liquid 31 during filling of thesecond liquid 32 in the inner space 216. Hence, with the inclusion ofthe first liquid 31 of the magnetic ink in the electrowetting device ofthis invention, a highly reliable electrowetting device may be obtained.

While the present invention has been described in connection with whatare considered the most practical and preferred embodiments, it isunderstood that this invention is not limited to the disclosedembodiments but is intended to cover various arrangements includedwithin the spirit and scope of the broadest interpretation andequivalent arrangements.

What is claimed is:
 1. An electrowetting device comprising: aliquid-confining member including a base and an electrode unit supportedon said base, said liquid-confining member defining an inner chamber; afirst liquid of a magnetic ink disposed in said inner chamber; and asecond liquid of a polar material disposed in said inner chamber andimmiscible with said first liquid, said first and second liquidscontacting each other to define a liquid-liquid interface therebetween;wherein said electrode unit is adapted to be connected to an externalpower source for providing an electric field across said liquid-liquidinterface; and wherein said liquid-liquid interface has a shape thatvaries in response to a change in the electric field across saidliquid-liquid interface.
 2. The electrowetting device of claim 1,wherein said first liquid includes magnetic pigment particles and anonpolar solvent.
 3. The electrowetting device of claim 2, wherein saidmagnetic pigment particles have an average particle size of not greaterthan 50 nm.
 4. The electrowetting device of claim 2, wherein saidmagnetic pigment particles are made from hydrophobic group modifiedferric oxide.
 5. The electrowetting device of claim 1, wherein saidliquid-confining member further includes a cover covering said base,said base including; a lower substrate that is opposite to said cover ina vertical direction; a surrounding barricade which extends from saidlower substrate in the vertical direction and which cooperates with saidlower substrate to define an inner space therebetween; and a hydrophobiclayer formed in said inner space, said electrode unit including a lowerelectrode provided on said lower substrate, and an upper electrodeprovided on said cover.
 6. The electrowetting device of claim 5, whereinsaid base further includes a hydrophilic wall which extends between saidsurrounding barricade and said cover and which cooperates with saidcover, said hydrophobic layer and said surrounding barricade to definesaid inner chamber.